米国の36空港で244のフルボディ "後方散乱" X線スキャナーが使用中である。運輸保安局ＴＳＡによると、ほぼノンストップで動作している。|
X-Ray Scans at Airports Leave Lingering Worries
By RONI CARYN RABIN
AUGUST 6, 2012, 5:26 PM
Even before she was pregnant, Yolanda Marin-Czachor tried to avoid the full-body X-ray scanners that security officers use to screen airport passengers. Now she’s adamant about it: She’ll take a radiation-free pat-down instead any day.
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“I had two miscarriages before this pregnancy,” Ms. Marin-Czachor, a 34-year-old mother and teacher from Green Bay, Wis., recalled, “and one of the first things my doctor said was: ‘Do not go through one of those machines. There have not been any long-term studies. I would prefer you stay away from it.’ ”
There are 244 full-body “backscatter” X-ray scanners in use at 36 airports in the United States. They operate almost nonstop, according to the Transportation Security Administration. Other airports use millimeter wave scanners, which look like glass telephone booths and do not use radiation, or metal detectors.
Most experts agree that as long as the X-ray backscatter machines are functioning properly, they expose passengers to only extremely low doses of ionizing radiation.
But some experts are less sanguine, and questions persist about the safety of using X-ray machines on such a large scale. A recent study reported that radiation from the machines can reach organs through the skin. In another report, researchers estimated that one billion X-ray backscatter scans per year would lead to perhaps 100 radiation-induced cancers in the future. The European Union has banned body scanners that use radiation; it is against the law in several European countries to X-ray people without a medical reason.
The machines move a narrowly focused beam of high-intensity radiation very quickly across the body, and David Brenner, director of the Center for Radiological Research at Columbia University Medical Center, says he worries about mechanical malfunctions that could cause the beam to stop in one place for even a few seconds, resulting in greater radiation exposure.
For security reasons, much about how the machines work has been kept secret. The T.S.A. says the full-body scanners have been assessed by the Food and Drug Administration, the United States Army Public Health Command and the Johns Hopkins University Applied Physics Laboratory.
But researchers at these institutions have not always had direct access to the scanners in use, and some of the published reports about them have been heavily redacted, with the authors’ names removed. Independent scientists say limited access has hampered their ability to evaluate the systems.
John Sedat, emeritus professor of biochemistry and biophysics at the University of California, San Francisco, believes that the effective dose could be 45 times as high as the T.S.A. has estimated, equivalent to about 10 percent of a single chest X-ray.
T.S.A. officials scoff at scientists’ statements that measuring the effective radiation dose received by passengers is very complex, saying that it is not difficult, that the machines are inspected for problems at least once a year, and that they are equipped with fail-safe shutoff systems.
The machines, though, have had mechanical problems. A recent T.S.A. report said that between May 2010 and May 2011, there were 3,778 service calls concerning mechanical problems in backscatter X-ray machines. Radiation safety surveys were conducted after only 2 percent of the calls.
In a letter to the federal Department of Health and Human Services dated Oct. 12, 2010, the scientists said that “the casual nature for maintenance of these devices is alarming to us. These machines are capable of delivering large X-ray doses.
They added, “Hospitals usually check for problems on X-ray machines daily.”
Most of what is known of the risks of radiation has been extrapolated from disease trends in Japan after World War II.
T.S.A. officials say that these low doses of radiation are safe for everyone, including pregnant women, infants and young children, even though children are significantly more sensitive to radiation’s effects.
Those at greatest risk, however, may be T.S.A. employees and others who work in the terminals and go through security daily. A 2004 National Institute for Occupational Safety and Health study of T.S.A. baggage screeners urged the agency to have employees wear film badges to monitor ongoing exposure systemically, as many hospital and lab employees do, and to label machines more prominently. The agency has not done so.
Marquette University study shows radiation from airport scanners extends into organs
The Business Journal by Rich Rovito
Date: Monday, June 11, 2012, 10:51am CDT
A study by the Marquette University College of Engineering concludes that the radiation dose from full-body backscatter X-ray scanners in airports extends to organs beyond the skin, but is still lower than health standards.
The study is the first nongovernment funded research to estimate the amount of radiation to individual organs. The research was conducted by Taly Gilat Schmidt, an assistant professor of biomedical engineering at Marquette, and Michael Hoppe, a Marquette graduate student.
The study estimates the radiation exposure to 29 organs ? including skin, eye lens, heart and the brain ? using complex mathematical models that more accurately represent the shape and tissue density of human bodies and organs. By comparison, previous studies funded through the Transportation Security Administration used more simplified, generic mathematical models, according to Marquette.
The Marquette study used four models: a 34-year old male, a 26-year-old female, an 11-year old female and a 6-year-old male. Although radiation is deposited beyond the skin, the study concludes radiation doses in organs for all four models is below recommended standards and considerably lower than radiation levels of other x-ray procedures, such as a mammogram.
Gilat Schmidt noted that independent research currently is based on data available from the TSA.
“Access to the machines for measurements and assessments is limited. Public disclosure of the systems specifications would enable more accurate system modeling,” Gilat Schmidt said.
The paper is currently available online and will be published in the June issue of Medical Physics, an international journal of medical physics research and practice, produced by the American Association of Physicists in Medicine.
Two types of scanners are currently being used in airports by the TSA: the backscatter X-ray and the millimeter wave scanner. The backscatter-type machines use low-level ionizing radiation to create two-sided images. Wave scanners use radio waves, instead of ionizing radiation, to create three-dimensional images.
Radiology. 2011 Apr;259(1):6-10.
Are x-ray backscatter scanners safe for airport passenger screening? For most individuals, probably yes, but a billion scans per year raises long-term public health concerns.
Center for Radiological Research, Columbia University Medical Center, 630 W 168th St, New York, NY 10032, USA. firstname.lastname@example.org
PMID: 21436091 [PubMed - indexed for MEDLINE]
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